In producing a glass bottle, a crack such as crazing may be sometimes formed in a wall thickness of a bottle-mouth portion. This crack is referred to as a check. Some glass bottles are manufactured as returnable bottles that are retrieved for reuse after they have been used. Returnable bottles are likely to have checks at their bottle-mouth portions when they are brought into contact with each other or with other objects while in use or transport. Glass bottles, regardless of whether they are newly produced bottles or returnable bottles, tend to have checks in limited regions of the bottle-mouth portions. Typically, there are a check generated in the top surface or near the top surface of the bottle mouth, a check generated in a screw thread portion of the bottle mouth, and a check generated in a skirt portion of the bottle mouth. Further, depending on the direction of the crack, the checks are classified into a vertical check extending in a vertical direction (substantially vertical direction) and a lateral check extending in a lateral direction (substantially horizontal direction).
Because the above-mentioned check can cause damage to the glass bottle, the presence or absence of a check is detected by imaging the bottle-mouth portion, and the glass bottle having the check is removed as a defective bottle.
Heretofore, there has been known a glass bottle inspection apparatus for automatically inspecting a glass bottle by imaging a bottle-mouth portion of a glass bottle to detect whether there is a check or not. The known glass bottle inspection apparatus has a single illuminating unit disposed above the bottle-mouth portion of a glass bottle and a number of (e.g., seven) cameras disposed around the bottle-mouth portion so as to surround the bottle-mouth portion. Scattered light emitted from the illuminating unit is applied to the bottle-mouth portion of the glass bottle, and if there is a check, the light is reflected by a crack plane of the check and is thus illuminated brightly. Therefore, images captured by the cameras include a brighter image area corresponding to the check than other image areas. The brighter image area is detected by image processing and judged as a check.